How can I render with RenderMan in the GPU, in Blender 2.76?
Renderman currently doesn't have GPU support:

Does Non-Commercial RenderMan support GPU's?
The current version of Non-Commercial RenderMan is a multi-threaded software application that does not use GPU's due to the current fluidity of graphics hardware and supporting software standards. However GPU's are an important aspect of the future direction of rendering that Pixar is currently researching, some of which has already demonstrated in public. As the technology matures for comprehensive production usage we will reveal more in future.

EDIT For the new Renderman 21, there is a separate Technical FAQ which adds the sentence

For the first time, RenderMan 21 introduces GPU accelerated denoising, and as GPU's mature for comprehensive production usage, we will reveal more in future.